1. Field of the Invention
The present invention relates to an ophthalmic apparatus.
2. Description of Related Art
In recent years, there have been more and more cases of performing laser refractive surgery in which a corneal stroma is ablated with an excimer laser beam to change a curvature of a corneal anterior surface for correcting a refractive error of an eye. Lately, a new type of surgery has begun to be performed to seek further improvement in visual acuity by measuring wavefront aberration of an eye and controlling ablation to correct the aberration. In this type of laser refractive surgery, wavefront aberration or a corneal shape is measured before the surgery.
However, the apparatuses for measuring wavefront aberration or a corneal shape take measurements with reference to a line of sight of an eye linking the center of the entrance pupil to a fixation point, or with reference to a keratometric axis, not a visual axis of the eye linking the central fovea to the fixation point through nodal points. In addition, a conventional laser corneal surgery apparatus performs ablation with reference to an approximate center of the pupil (if the eye to be operated on is fixating a fixation light source located on an optical axis, it means that the ablation is performed with reference to the line of sight), not the visual axis, either. It follows then that the measurement is made based on an axis different from the visual axis given when the eye is actually looking at an object, and that the wavefront aberration is corrected based on that different axis, and an expected visual acuity may not be obtained if the difference is large.